Multi-fuel vehicles are known. For example, cars with spark-ignition engines (Otto cycle) have been outfitted with natural gas and propane fuel capability so that they can run on gasoline, or switch and run on either natural gas or propane. These engines can be switched on the fly (that is when the engine is running and the vehicle is in motion). There is, however, a limitation on this multi-fuel capability since the fuels must have comparable ignition characteristics. The fuels must have a high enough octane rating such that they are ignited as prescribed by the spark ignition system and not pre-ignited such as by compression or hot surfaces before the prescribed spark ignition.
Some trucks are available with diesel engines (Diesel cycle) and can run on diesel fuel or a mixture of diesel fuel and natural gas fuel. In the latter case, the natural gas is the predominant fuel and the diesel fuel is utilized as an ignition fuel. Unlike natural gas fuel, diesel fuel has excellent compression ignition characteristics but the combination of diesel fuel and natural gas fuel can be made to combust at the prescribed time of the combustion cycle.
Some fuels, such as gasoline and diesel fuel, are widely available for use in vehicles through a well-developed distribution infrastructure. These fuels are well characterized in terms of ignition characteristics, cost, energy content and emissions.
Other fuels, such as natural gas, bio-diesel, ethanol, methanol, butanol, propane and hydrogen, are less readily available for use in vehicles but may have cost and emissions advantages over the widely available fuels.
For example, there is a distribution infrastructure for natural gas though this infrastructure is less developed for vehicles than for distribution to fixed commercial users. Both liquefied natural gas (“LNG”) and compressed natural gas (“CNG”) forms of natural gas are available to vehicles as fuels on a limited basis. Refueling an LNG-powered vehicle is often problematic since it requires special equipment and special procedures, which are not always convenient for vehicle operators.
There is currently a very limited infrastructure for hydrogen fuel. However, if hydrogen fuels were available, they would have excellent emissions characteristics (no greenhouse carbon emissions at the point of use). As with natural gas, refueling would require special equipment and special procedures, which may not be convenient for vehicle operators.
The problem faced by developers of any new fuel is that they require a widely available distribution infrastructure for a new fuel to become accepted. However, the costs and risks of installing such an infrastructure may be too great until acceptance of the new fuel can be demonstrated. In addition, the introduction of a new fuel will inconvenience vehicle operators if the new fuel requires new procedures and/or new equipment or is not readily available.
There therefore remains a need for innovative strategies for introducing and dispensing new fuels for vehicles that can operate on any of several fuels where such introduction does not depend on a pre-existing well-developed distribution infrastructure and where such introduction can be made seamless to the vehicle operator.